Straightening elongated articles

ABSTRACT

This specification discloses a method and apparatus for straightening a bent elongated article of substantially constant cross-section in which the article is constrained to take up a straight configuration by holding it at both ends and applying a force to it by means of a die in a direction substantially at right angles to the longitudinal axis of the article intermediate its ends and the article is twisted about its longitudinal axis so that sufficient of the material of the article is plastically strained in torsion in order that when the article is released from constraint the article retains the straight configuration.

United States Patent [191 Townend STRAIGHTENING ELONGATED ARTICLES [75]Inventor: Gordon Howard Townend,

Wolverhampton, England [73] Assignee: GKN Group Services Ltd.,

Worcestershire, England 22 Filed: Aug. 8, 1973 [21] Appl. No.: 386,799

[451 May 20, 1975 Primary Examiner-C. W. Lanham Assistant Examiner-M, J.Keenan Attorney, Agent, or Firm-A, Yates Dowell, Jr.

[57] ABSTRACT This specification discloses a method and apparatus forstraightening a bent elongated article of substantially constantcross-section in which the article is constrained to take up a straightconfiguration by holding it at both ends and applying a force to it bymeans of a die in a direction substantially at right angles to thelongitudinal axis of the article intermediate its ends and the articleis twisted about its longitudinal axis so that sufficient of thematerial of the article is plastically strained in torsion in order thatwhen the article is released from constraint the article retains thestraight configuration.

3 Claims, 5 Drawing Figures STRAIGHTENING ELONGATED ARTICLES BACKGROUNDOF THE INVENTION 1. Field of the Invention This invention relates tomethods and apparatus for straightening elongated articles ofsubstantially constant cross-section.

2. Description of the Prior Art Various methods other than pure bendinghave been proposed for straightening elongated articles. Thus, forexample, it is known to straighten longer articles, such as drill tubes,by applying localised bending moments to the tube while rotating thetube. The localised bending moments may be applied by moving a carriagelongitudinally of the article, the carriage having pads or rollers forengaging the article as the article is rotated.

It is also known to apply a tensile force to an article in directionsparallel to the longitudinal axis thereof to remove an axial bow or bendtherein. A high tensile force is required since the force acts along aline not far removed from the centroid of the section at the point ofmaximum bow. The induced bending moment is therefore low and in orderfor the bending movement to be sufficient to straighten the article thetensile force may in many instances be so high as to cause permanentelongation of the article with a consequent reduction in cross sectionwhich is not permissible in many cases.

It has also been proposed to twist an elongated article when undertension to remove an undesired skew relationship between the ends of thearticles.

In order to improve the mechanical properties of an elongated articlesuch as a reinforcing bar, it has been proposed to cold work the articleby twisting it about its longitudinal axis. During this twisting the barmay be under tension which is likely to cause the bar to elongate. Whilewith an article such as a reinforcing bar, a small elongation andreduction in section is acceptable, this is not acceptable for smallerparts with small tolerances.

In French Patent Specification No. 860,100 there is described a methodof cold working a bar to improve its mechanical properties by bendingthe bar into a bowed shape and then rotating the bar so that eachsection rotates about an axis which is generally tangential to the curveof the bow. The specification makes it clear that in order to improvethe mechanical properties there must be plastic deformation which ofcourse will accompany the cold working. The specification states thatthe plastic deformation may either be in bending or in torsion. Wherethe plastic deformation is in bending then both ends of the bar can berotated at the same speed and after cold working the bar has to berestraightened if a straight bar is required. On the other hand, if thebar is bent within the elastic range and is subjected to plastictorsion, it is stated that one of the advantages of this arrangement isthat restraightening of the bar is not necessary, the inference beingthat the bar will spring back to its straight position after thetwisting has been completed.

Contrary to what is stated in the French specification we havesurprisingly discovered that if an elongated article is subjected toplastic strain in torsion the longitudinal axis of the article will takea permanent set in the configuration which it has when the plasticdeformation in torsion is effected.

It is an object of the present invention to provide a method ofaccurately straightening an elongated article without the reduction incross-section and elongation discussed above.

SUMMARY OF THE INVENTION According to one aspect of the presentinvention I provide a method of straightening a bent elongated articleof substantially constant cross-section comprising the steps ofconstraining the article to take up a straight configuration by holdingthe article at both ends and applying a force to the article in adirection substantially at right angles to the longitudinal axis of thearticle intermediate its ends and twisting the article about itslongitudinal axis so that sufficient of the material of the article isplastically strained in torsion in order that when the article isreleased from constraint the article retains the straight configuration.

The invention is primarily concerned with the straightening of partswhere high accuracy is required, for example, a total indicator readingof not more than 0.010 inches. TIR readings are obtained by placing aclock gauge in contact with the point of largest bow on the article androtating the article, while it is supported at both ends, through 360.These readings are thus equal to twice the largest bow. More accuratestraightening than this can easily be obtained using the invention.

The invention has been developed in connection with the straightening ofbolt blanks before the blanks are threaded but is not limited theretoand can be applied to other articles such as connecting rod blanks.

A bent elongated article may possess a number of bend conditions. Forexample, the article may have a steady bend of large radius of curvatureor a sharp bend of locally small radius of curvature. The article mayalso be bent in a single plane or may include a number of bends indifferent planes.

It is extremely difficult to provide an apparatus or a method which willstraighten a bent elongated article including any one of the bendconditions described above and which is capable of giving the degree ofaccuracy of 0.010 inch TIR discussed above coupled with the capabilityof automatic operation to give the level of output necessary to make itcommercially viable.

In order to illustrate this point, an example will now be given of thedifficulties involved in straightening a bolt blank, by conventionalbending methods, which possesses the simplest bend condition of a steadybend in one plane. The problem arises from the elastic recovery of thebolt blank material after it has been deformed. Thus, if one has a bentbolt blank it is insufficient merely to bend the blank to a straightconfiguration because when the forces bending the blank are released theblank will spring back to its bent configuration. It is thus necessaryto overbend the blank so that after elastic recovery has taken place thelongitudinal axis of the blank is straight. It is apparent that in orderto straighten the blank the material thereof must be caused to flowplastically and one requires a considerably greater deflection of theblank to cause plastic flow than is required to actually straighten theblank. Thus, for example, to correct a deflection of, say, 0.020 inch ata point on the blank it may be necessary to deflect the blank by, say,three-eighths inch in order to obtain plastic flow of the material andthen continue the deflection by the 0.020 inch to change theconfiguration of the axis. The actual straightening part of thedeflection is therefore only a small part of the total deflection whichis required and this makes for difficulties in practice instraightening.

The difficulties encountered in straightening an elongated article witha number of bends in different planes are even more complex as each bendmust be straightened separately using the above bending technique.

I have found that by constraining an elongated article to take up astraight configuration and plastically straining the article in torsionwhen so constrained, the plastic strain induced by the torsion willeffectively kill the elastic recovery of the article in bending so thatthe article will retain the straight configuration when released fromconstraint. It is not necessary that the article is plastically strainedacross its whole crosssection perpendicular to the longitudinal axis.The amount of the cross-section which is plastically strained must besufficient to cause the article to retain the straight configurationwhen the constraint is released. It may be, for example, that theplastic straining of the outer half of the cross sectional area of thearticle is sufficient for this purpose.

The invention thus provides an efficient method of straightening anelongated article with bends in one or more planes. The method andapparatus in accordance with the invention can also readily be automatedand are easily capable of producing the level of accuracy discussedabove.

The method may be carried out by clamping the article at both ends, oneend being clamped so as to hold it stationary and the other end beingclamped so as to permit twisting of the article about its longitudinalaxis, bringing a die into engagement with a portion of the articlebetween the clamped ends so as to constrain the article to take up astraight configuration, and twisting said other end of the article whenso constrained so as to plastically strain the article in torsion.

Although the deformation of the article in bending by the die willnormally be within the elastic range, this deformation may in certaincases be plastic, for example, when the article is badly bent the forcesexerted on the article by the die in constraining the article to take upa straight configuration may in fact result in plastic deformation ofthe article. However, for the reasons explained above, this plasticdeformation in bending will not itself be sufficient to permanentlystraighten the bar.

Where the ends of the article must remain in some predeterminedrelationship to one another, for example in the case ofa connecting rod,then the article may be twisted in one direction to strain itplastically and then twisted back in the opposite direction also toobtain plastic strain and to bring the ends of the article back into thedesired relative relation.

The invention also provides apparatus for straightening a bent elongatedarticle of substantially constant cross-section comprising means forholding the article at both ends and a die arranged to contact thearticle intermediate its ends so as to apply a force to the article in adirection substantially at right angles to the axis of the article thisconstraining the article to take up a straight configuration, one ofsaid holding means being rotatable and the other fixed so that thearticle can be plastically strained in torsion about its longitudinalaxis when constrained by the die.

The die may be in two parts arranged to be brought into contact with thearticle from opposite sides thereof, the die parts being provided withformations which contact the article to constrain it but allow it to betwisted while constrained.

For example, if the article to be straightened is of circularcross-section the die parts may be provided with formations in the formof grooves of V-shaped crosssection which extend longitudinally relativeto the article and which co-operate to define a closed channel ofsubstantially square cross-section in which the article is constrained.

Conversely, if the article is square in cross-section it may beconstrained in a closed channel which is circular in cross section.

One of the parts may be arranged to be brought into contact with a stopthus positioning said part in a predetermined position relative to theclamped ends of the article and the other die part may be arranged to bebrought into contact with said one die part so as to constrain thearticle.

BRIEF DESCRIPTION OF THE DRAWINGS One embodiment of the invention willnow be described, by way of example, with reference to FIGS. 1 to 5 ofthe accompanying drawings in which:

FIG. 1 is a longitudinal section through part of an apparatus embodyingthe invention;

FIG. 2 is a sectional view on the line AA of FIG.

FIG. 3 is a view in the direction of the arrow B in FIG. 1 of one end ofthe apparatus shown in FIG. 1; and

FIGS. 4 and 5 are side and plan views respectively of the other end ofthe apparatus shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT The invention will be describedin relation to the straightening of a bolt blank which is indicatedgenerally at 10 in FIG. 1 and which has a shank 11 of constant andcircular cross-section and a bolt head 12 which is generally spherical.

The apparatus for straightening the bolt blank comprises a base plate 13which carries at its right hand end a clamping block 14 mounted on adove-tail crosssection slide 15. At the other end of the base plate arotatable chuck 16 is mounted on bearing assemblies 17 and 18, see FIG.4. Positioned intermediate the clamping block 14 and rotatable chuck 16is a two-part die arrangement 19, see FIG. 2.

The die arrangement comprises two die parts 20 and 21 which are mountedon dove-tail cross-section slides 22 and 23 respectively which in turnengage corresponding dove-tail cross-section slides 24 and 25 which aresecured to the base plate 13. As can be seen from FIGS. 1 and 2, the dieparts 20 and 21 are arranged to be brought into contact with the boltblank from opposite sides of the blank. Both die parts are provided withV-shaped cross-section grooves 26 and 27 respectively which extendlongitudinally relative to the bolt blank and which co-operate to definea closed channel of substantially square cross section in which the boltblank may be constrained into a straight configuration.

The die parts are moved on the slides 24 and 25 by hydraulic piston andcylinder arrangements (not shown), the movement of the die part 20 beinglimited by an adjustable stop 28. The V-shaped cross section groove 26provided in the die part is deeper than the corresponding groove 27provided in die part 21 and the outer surfaces 29 and 30 of the die part21 are chamfered so as to enter the groove 26. The die part 21 isresiliently mounted on the slide 23 by a number of pre-loaded Bellevillewasher arrangements 31 spaced along the die part. Each Belleville washerarrangement comprises a stack of Belleville washers 32 encircling a bolt33, one end of the bolt being screwed into the slide 23 and the headedend of the bolt being received in a recess 33a provided in the die part21.

As can be seen from FIG. 2, the pre-loaded Belleville washerarrangements 31 force the die part 21 away from the slide 23 and leave agap 34 therebetween. By chamfering the die part 21 and resilientlymounting this die part on the slide 23 the two-part die arrangement ismade self-aligning as when the die part 21 contacts the die part 20, thechamfered surfaces 29 and 30 enter the groove 26 and the resilientmounting of the die part 21 allows this part limited freedom to movevertically and also to rotate relative to the other die part 20 about anaxis substantially parallel to the bolt blank so that the two die partsautomatically align themselves so as to constrain the bolt blank in thedesired manner. The piston and cylinder arrangement which brings the diepart 20 into contact with the stop 28 is arranged to exert a greaterforce than the piston and cylinder arrangement which brings the die part21 against the die part 20. This ensures that the die part 20 alwaysprovides the fixed reference for the die part 21.

The clamping block 14 includes a lower jaw 35 and an upper jaw 36 whichis mounted for vertical sliding movement on slides 38. The lower jaw 35extends further towards the chuck 16 than the upper jaw 36 thusproviding a ledge 53 which extends beyond the upper jaw 36. The clampingaction is provided between the upper and lower jaws by an hydraulicpiston and cylinder assembly 37 which is connected to the upper jaw 36and which raises and lowers the upper jaw. An hydraulically operatedejector 39 is provided for assisting in the removal of the bolt blankfrom the apparatus when the headed end of the blank is released from thechuck 16. The ejector comprises a push rod 40 which is aligned with theend of the bolt blank, the push rod being arranged to contact the boltblank and push it onto the ledge 53 when the headed end of the boltblank is released following a straightening operation.

As previously stated the clamping block 14 is mounted on a slide 15 ofdovetailed cross-section. This allows the apparatus to be used tostraighten bolt blanks of varying lengths, as the distance between thechuck 16 and clamping block 14 is readily adjustable by sliding theclamping block 14 on the slide 15 and locking the clamping block in therequired position by clamping means, not shown.

The rotatable chuck 16 is secured to an outer shaft 41 by an internallythreaded retaining ring 42 which engages a screw-threaded shoulder 43provided on the outer shaft. The outer shaft is supported on axiallyspaced bearing assemblies 17 and 18 which are carried by a housing 44which is secured to the base plate 13. As can be seen from FIGS. 4 and5, the chuck 16 is provided with a key-hole shaped access aperture 45through which the head 12 of the bolt blank may be inserted. When inposition in the chuck 16, the head 12 of the bolt blank is clampedagainst part-sperical surfaces 46 provided in the chuck by an innershaft 47 which extends within a bore 48 provided in the outer shaft 41and is supported in this bore by plain bearings 49 which allow the innershaft limited freedom to move within the outer shaft so as to alignitself correctly with the head of the bolt blank. The end of the innershaft is recessed so as to co-operate with the head of the bolt blankand the inner shaft is pressed against the head of the bolt blank by ahydraulic piston and cylinder assembly 50 which rotates with the outershaft 41.

The outer shaft 41 is rotated by a rack 51 which cooperates with apinion 52 carried by the outer shaft. The rack 51 is moved by ahydraulic piston and cylinder assembly 53.

The apparatus described above operates as follows: The head 12 of a boltblank 10 is placed in the chuck l6 and the end of the shank 11 of theblank is placed on the ledge 53 provided on the lower jaw 35 of theclamping block. The hydraulic piston and cylinder assembly 51 is thenactuated so as to clamp the head of the bolt blank in the chuck 16 andto push the end of the bolt shank further onto the lowerjaw 35. Pistonand cylinder assembly 37 is then actuated to bring the upper jaw 36 intoclamping engagement with the end of the shank. The die part 20 is thenadvanced the bolt shank 10 until the stop 28 is contacted. The other diepart 21 is then brought towards the die part 20 until the chamferedsurfaces 29 and 30 enter the groove 26 in the die part 20 and the dieparts automatically align themselves as previously described. Byadjusting the position of the stop 28 prior to the commencement of thestraightening operation, the die parts 20 and 21 can be arranged toconstrain the bolt blank 10 to take up a straight configuration.

While the bolt blank is so constrained, the chuck 16 is rotated by theactuation of the piston and cylinder assembly 53. This subjects the boltblank to torsion, the rotation of the chuck 16 being arranged to besufficient to plastically strain sufficient of the cross-section of thebolt blank so as to cause the blank to retain its straight configurationwhen released from constraint by the die parts 20 and 21.

Following the twisting of the bolt blank, the piston and cylinderassemblies 50 and 37 are retracted so as to release the ends of the boltblank and the die parts 20 and 21 are drawn away from the blank. Theejector 39 is then actuated to assist in the removal of the bolt blankfrom the chuck and clamping block.

The precise shape of the chuck 16, the two-part die arrangement 19 andthe clamping block 14 is determined by the shape of the article which itis desired to straighten. The apparatus described above can thus be usedto straighten a variety of articles by employing a suitably shapedchuck, two-part die arrangement and clamping block or by replacing thechuck 16 by an appropriately shaped clamping means which is capable ofthe necessary rotation.

Where the ends of the article to be straightened must remain in somepredetermined relationship to one another, for example in the case of aconnecting rod, then the article may be twisted in one direction tostrain it plastically and then twisted back in the opposite directionalso to obtain plastic strain and to bring the ends of the article backinto the desired relationship.

Experimental results obtained using the apparatus described above tostraighten bolt blanks are shown in Table I below. The table shows thetotal indicator readings (TIR) obtained before and after the bars hadbeen straightened by twisting through an angle of 120.

TABLE I.

TlR VALUES (inches) Before Straightening After Straightening To givesome indication of the efficiency of the invention a similar set of boltblanks were straightened by plastically straining the blanks in tension.The blanks were subjected to a 0.2 per cent tensile strain and theresults achieved as set out below in Table II.

TABLE II.

TlR VALUES (inches) Before Straightening After Straightening I08 .022103 .025 100 .007 .092 .O l 7 apparatus for straightening a bentelongated article which, as can be seen from Table i, are capable ofworking to a very high degree of accuracy.

The apparatus described above may easily be arranged for automaticoperation by providing a mechanical handling device to place the head ofthe bolt blank in the chuck l6 and the end of the bolt shank l 1 on theledge 54 and to remove the bolt blank from the chuck and ledge when thestraightening operation has been completed.

I claim:

1. A method of straightening an elongated article having a bent portionof substantially constant crosssection comprising the steps of clampingthe article at each end so as to hold one end stationary while the otherend is clamped so as to permit the end to be twisted about thelongitudinal axis of the article, bringing a die into engagement withsaid portion of the article so as to constrain said portion of thearticle to take up a straight configuration without preventing twistingthereof about said axis, and twisting said other end of the articleabout said axis while said portion is so constrained to plasticallystrain sufficient of the material of said portion in torsion wherebywhen said portion is released from constraint said portion retains itsstraight configuration.

2. A method as claimed in claim 1 comprising bringing two die parts intoengagement with said portion of the article from opposite sides thereofin order to constrain the article.

3. A method as claimed in claim 2 comprising bringing one of the dieparts into engagement with a stop, thereby positioning said part in apredetermined position relative to the clamped ends of the article, andbringing the other die part into contact with said one die part so as toconstrain said portion of the article.

1. A method of straightening an elongated article having a bent portionof substantially constant cross-section comprising the steps of clampingthe article at each end so as to hold one end stationary while the otherend is clamped so as to permit the end to be tWisted about thelongitudinal axis of the article, bringing a die into engagement withsaid portion of the article so as to constrain said portion of thearticle to take up a straight configuration without preventing twistingthereof about said axis, and twisting said other end of the articleabout said axis while said portion is so constrained to plasticallystrain sufficient of the material of said portion in torsion wherebywhen said portion is released from constraint said portion retains itsstraight configuration.
 2. A method as claimed in claim 1 comprisingbringing two die parts into engagement with said portion of the articlefrom opposite sides thereof in order to constrain the article.
 3. Amethod as claimed in claim 2 comprising bringing one of the die partsinto engagement with a stop, thereby positioning said part in apredetermined position relative to the clamped ends of the article, andbringing the other die part into contact with said one die part so as toconstrain said portion of the article.